Question

The exhaust steam from a power station turbine is condensed in a condenser operating at 0.0738 bar(abs). The surface of the heat transfer surface is held at 20°C. What percentage change does the inclusion of the sensible heat correction term make to the estimated heat transfer condensing film coefficient?

Answer 1

Percentage change 5.75 %.

Explanation:Given ;

Given

Pressure of condenser =0.0738 bar

Surface temperature=20°C

Now from steam table

Properties of steam at 0.0738 bar

Saturation temperature corresponding to saturation pressure =40°C

`h_f= 167.5(KJ)/(Kg),h_g= 2573.5(KJ)/(Kg)`

So Δh=2573.5-167.5=2406 KJ/kg

Enthalpy of condensation=2406 KJ/kg

So total heat=Sensible heat of liquid+Enthalpy of condensation

`Total\ heat\ =C_p\Delta T+\Delta h`

Total heat =4.2(40-20)+2406

Total heat=2,544 KJ/kg

Now film coefficient before inclusion of sensible heat

`h_1=(\Delta h)/(\Delta T)`

`h_1=(2406)/(20)`

`h_1=120.3(KJ)/(kg-m^2K)`

Now film coefficient after inclusion of sensible heat

`h_2=(total\ heat)/(\Delta T)`

`h_2=(2,544)/(20)`

`h_2=127.2(KJ)/(kg-m^2K)`

`So\ Percentage\ change=(h_2-h_1)/(h_1)* 100`

`=(127.2-120.3)/(120.3)* 100`

=5.75 %

So Percentage change 5.75 %.